The ability of shape-memory metals to change from one shape to another has been used in a variety of applications. The discovery of a new category of shape-memory materials made of ceramic rather than metal could open up a new range of applications.
The paper by Edward Pang, who was a PhD student at MIT, will be published in the journal Nature.
Schuh says that shape-memory materials have two different shapes and can change between them. He says that they can be triggered by temperature, mechanical stress, or electric or magnetic fields to change shape.
He says that they are interesting because they are a device that can push against something Ashape-memory material is a solid state material that does all of that. It does not require a system. It doesn't require a lot of parts. It's just a material that can change its shape. It can do something. It is interesting as a smart material.
It is possible to use shape-memory metals in a variety of devices but they are limited by the service temperatures of the metals used. Ceramics are known for their brittleness even though they can tolerate higher temperatures. The MIT team has found a way to make a ceramic material that can actuate without accumulating damage, which will allow it to function reliably as a shape-memory material through many cycles of use.
Schuh says thatshape-memory materials are all metal. There's a lot of damage that can be done when you change a material's shape. The structure of the atom needs to be changed. As atoms are moving and reshuffling, it's easy to get them in the wrong spots and cause defects and eventually fall apart.
He says that materials that can change a few times can degrade and fall apart. The field has focused on metals because they are more resistant to damage than other metals.
Ceramics don't allow damage at all and don't bend but break. It accumulates damage very easily during a shape memory cycle when it has a shape-memory property. We wanted to design a new ceramic that targets that hysteresis. The shape of the ceramic is so large that we want to do a lot of work. It's more gentle at the atomic level.
Schuh says that Pang put all of the modern tools of science together in a completely new way.
There was a new variation of the metal. Schuh said it was zirconia. It looks and tastes similar to zirconia that people already know and use. Some elements have been introduced into its structure in a way that affects its properties. The elements make the lattice more gentle at the atomic scale by dissolving into it.
Schuh says that the hysteresis is now similar to metals. That change was a factor of 10. The rod of this material could get 10 percent longer when triggered, which is enough to do significant work.
Relief valves are a common application of shape-memory materials, where if a tank of something exceeds a certain critical temperature, the valve is triggered to open and relieve pressure. The new ceramic material is capable of handling much higher temperatures than the present materials can.
It might be useful to have a jet engine that has direct air flow. A shape-memory ceramic could be triggered by directing cooler or hotter air on the device if the environment there is hot.
Schuh says that today's shape-memory ceramics are curiosities because they fall apart after a few cycles. It's a step in the direction of making something that can operate many, many times in service.
The team plans to continue exploring the material, looking for ways to produce it in bigger batches and more complex shapes, and testing its ability to endure many cycles of transformation.
Schuh says that the project's potential for broad applications attracted him to it in the beginning. The idea that you can replace a complicated package of things with a single material that has the function built in at the atomic scale is attractive to me. Replacing vacuum tubes with transistors is similar to that.
Schuh says that it's hard to predict where this material will be used in the first place. It is difficult to make that on a small scale. There are a lot of applications for microscale motions because of the idea that you have a solid state version of that. Microrobots in small places, lab-on-a- chip valves, lots of small things that need actuation could benefit from smart materials.
More information: Christopher Schuh, et al. Low-hysteresis shape-memory ceramics designed by multimode modelling, Nature (2022). DOI: 10.1038/s41586-022-05210-1. www.nature.com/articles/s41586-022-05210-1 Journal information: Nature
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